The present invention relates generally to an apparatus for vibrating an article and, more specifically, to an economical electrodynamic vibrator for transducer test equipment.
Vibration of industrial machinery may be monitored by a system that includes a transducer and a measuring unit connected together by a cable. Test equipment for measuring the accuracy of such a system is well-known. The test equipment or test set includes a vibrator drive, often called a "shaker," which may be electrodynamic or electrohydraulic. The test set also includes an oscillator for exciting the shaker at a precisely regulated frequency and amplitude. To use the test set, an operator removes the transducer from the machinery on which it is mounted and mounts the transducer on the shaker while the transducer remains connected by its cable to its associated measuring unit. The shaker has a threaded spindle for facilitating mounting the transducer. The operator then activates the test set, which vibrates the transducer. The operator knows the frequency at which the test set is vibrating the transducer-under-test and can compare that value to the frequency measured by the measuring unit. The frequency and amplitude at which the test set vibrates may either be fixed or selectable by the operator. The test set may also measure other parameters, such as the acceleration, velocity, or sensitivity of the transducer-under-test. A reference accelerometer may be mounted on the shaker below the mounting spindle to measure the parameters or to provide a feedback signal to the oscillator. The test set typically includes a display for providing the measured parameters to the operator.
A typical electrodynamic shaker comprises a housing, a permanent magnet having a generally annular shape, and a wire coil armature assembly suspended within the opening in the magnet. The suspension comprises at least one leaf, often called a "spider," made of a stiff but resilient material such as plastic. Two such spiders, one at each end of the coil, may be used. The mounting spindle is attached to the armature. The components of such shakers are rugged yet built and assembled to precise tolerances. The precision armature assembly allows the shaker to produce a wide range of vibration frequencies, and the rugged structure allows the shaker to vibrate transducers having a wide range of weights. The manufacturing costs of producing such a shaker are correspondingly high. It would be desirable to provide a more economical shaker that may be used in test sets where extreme precision and wide frequency ranges are not critical requirements. These problems and deficiencies are clearly felt in the art and are solved by the present invention in the manner described below.